The present invention relates to a pressure-medium cylinder with pressure intensification, the pressure-medium cylinder having arranged in it two cylinders which are separate from one another and in each of which a piston is arranged, and the piston of the first cylinder having a piston rod which is operatively connected to the second cylinder for the increase in pressure, and to a use of such a pressure-medium cylinder as an adjusting cylinder in a roll stand, and also to a method for operating and regulating such a pressure-medium cylinder.
For specific applications, for example in roll stands, pressure-medium cylinders have to be capable of applying high forces and/or of being regulatable exactly in position. For this purpose, a pressure-medium cylinder, for example a hydraulic cylinder, with a piston of large cross section may be provided, and/or the pressure-medium cylinder must be supplied with pressure medium which is under high pressure. In the first instance, the pressure-medium cylinder becomes very large, and, in the second instance, the operation of the pressure-medium system involves a high outlay. Furthermore, where large cylinders are concerned, a large quantity of pressure medium has to be moved, with the result that the dynamics of such cylinders, that is to say the time for executing adjusting movements of the cylinder, are impaired.
DE 36 30 725 A, then, discloses, for example, a pressure intensification for increasing the pressure in the hydraulic supply line to a hydraulic cylinder. Here, however, the pressure intensifier operates pneumatically, thus necessitating two different supply media and the installations associated with this. The problems described above, however, cannot be solved by means of such pressure intensifiers.
WO 02/053920 A2 shows a hydraulic or hydropneumatic pressure intensifier which combines a low-pressure cylinder and a working cylinder in a housing. In such a pressure intensifier, however, the two pistons cannot be activated independently of one another. Only the low-pressure cylinder which transmits the movement to a working piston can be activated. This, however, also restricts the latitude of movement of the working cylinder, or large volumes and dimensions are again required, with the result that, once more, the dynamics would be impaired. Moreover, the pressure medium for the working cylinder is not supplied from outside, but is enclosed in the pressure intensifier, which may lead to problems with leakage losses, and the pressure medium has to be regularly topped up.
US 2002/0029569 Ai discloses a hydraulic working cylinder, in which a hydraulically activated pressure amplifier piston increases the hydraulic pressure on the working cylinder. In addition, a path measurement system for controlling the piston positions is described. In this case, however, the position of only one piston can be detected.
U.S. Pat. No. 5,207,267 discloses a cylinder which has two pistons operatively connected to one another. Each piston rod has its own measuring device, so a more complex measuring apparatus is required.